Sheet permanent magnet material is a well-established commercial product, and usually is made by mixing powdered high-permeability ferrite material into a uniform mixture with a suitable settable plastic vehicle. The mixture is converted into strip or sheet form, and the plastic vehicle is set to provide a permanent stable product that usually is somewhat flexible, and that can readily be handled and made into elements of any desired shape by cutting and/or stamping. The ferrite material is permanently magnetized so that the resulting elements can act individually as permanent magnets. The magnetic field of this material is of sufficient strength that the elements will adhere to a magnetizable metal surface, such as the surface of an iron or steel sheet, even through a sheet of paper or thin cardboard. A popular application of such materials is thin, flat magnets having on what is called for convenience in description their outer surface a decorative pattern and/or information, such as advertising. These magnets are adherable to the sheet steel door of a refrigerator, where they can also be used to hold sheets of paper, etc. thereon. Ferrites and the resultant sheet materials are inherently somewhat dark in colour, and therefore it is usual to cover the sheet outer surface with a thin layer of a lighter coloured material, usually a plastics material, on which the decorative patterns etc. can be printed. Another application for these elements is in a space planning kit as disclosed in my U.S. Pat. No. 5,505,620 issued Apr. 9, 1996.
A current method of manufacturing these magnetic elements involves the first step of screen printing symbols representative of the space planning elements onto a sheet of magnetic material. The next step is to is die cut or stamp out the elements along the symbol edges. While this two step process appears to be simple, it is a rather involved and requires considerable care by an operator to minimize wastage or scrap.
In the screen printing step a film is first produced of the desired image. A printing screen is then “shot” to have the image transferred to a screen. The non-image area is blocked out to prevent ink from being “pushed” through to the sheet. The screen is positioned on a press relative to registering stops that are used to hold the material in a set placement. If the screen press has a steel bed press surface, the user has to position an insulating sheet on the bed to prevent the magnetic sheet from interacting with the steel bed and interfering with proper positioning prior to printing. Ink is poured upon the screen after determining the proper viscosity for the desired resolution of the print image. After this set-up process, the magnetic substrate sheet is positioned against the register stops, and the print machine is activated, whereby the screen is automatically lowered, a squeegee is dragged over the screen, pushing ink onto the substrate. The screen is then lifted, and the process is repeated. The printed sheets are hand-removed, and placed on large drying racks, then stacked for transportation to a die cutter.
This screen printing step is cost efficient for a low number of sheet printing runs as compared to offset-press printing which has a cost benefit for sheet printing runs at around 300 sheets and up for each set-up. However, screen printing is slow and depending upon the resolution of the image needed, the screen image tends to get blocked up with dried ink, and has to be cleaned repeatedly. Further the above set-up procedure has to be repeated for each colour of a multi-coloured job, furthering the potential for waste or scrap. In this process, the amount of waste product becomes dependent on the skill of the operator particularly during the positioning of the sheet with the registering stops. The registration of the sheet during printing is critical and must always be in the same place for every print. If not, the sheet material is wasted during the die-cutting of the sheet as the precise location of the die cutting does not align with the screen printing borders for the symbols.
This screen printing step is manual and the operator requires, and acquires, a skill to accurately carry out the process. After a few set-ups, the monotony of the procedure results in the chances of operator error increasing with each sheet printed.
Further for multi-coloured projects that require consistency from colour-to-colour to get the image quality desired, the registration issues are more compounded when compared with one-colour jobs.
Because of the force needed to push the ink through the screen, the sheet may also be subject to stretching, which affects the image quality and accuracy when the sheet is die-cut.
After the screen print process, the printed sheet is sent to the die-cutters where the setup consists of installing a complex patterned die and the die is set to cut against the register or a “feed-corner” of the sheet. This is theoretically the exact same position that the screen printer used. This is where the registration inconsistencies and material deformation becomes apparent from sheet to sheet printed. In some instances this inconsistency in registration has resulted in scrapping as much as 10-15% of the printed sheets. The die cutting process is also a manual fed process. Due to the magnetic properties of the sheet, the die cutting step is subject to the same problematic issue with a steel bed as discussed above in the screen printing step.
An in-line, high speed manufacturing process of magnetic products is disclosed in U.S. Pat. No. 5,869,148 issued Feb. 9, 1999 to Silverschotz et al. This in-line process takes a substrate and applies printing to the substrate. The ink is dried and the substrate is scored. Next a magnetic slurry is applied to the substrate over the printing. The magnetic slurry is then magnetized and the sheets are cut to desired dimensions. This high speed manufacturing process requires, in addition to know how of printing and scoring, the know how of making the substrate into a magnetic substrate by the application of the magnetic slurry and subsequent magnetization of the substrate. It is a more complex and costly procedure for manufacturers of mid size and small runs who find it more practical to acquire sheets of permanent magnet materials and then screen print and die cut these sheets.